# std::ranges::views::as_rvalue, std::ranges::as_rvalue_view

From cppreference.com
< cpp‎ | ranges

Defined in header `<ranges>` |  |
template< ranges::view V > requires ranges::input_range<V> class as_rvalue_view : public ranges::view_interface<as_rvalue_view<V>> | (1) | (since C++23)
namespace views { inline constexpr /* unspecified */ as_rvalue = /* unspecified */; } | (2) | (since C++23)
Call signature |  |
template< ranges::viewable_range R > requires /* see below */ constexpr ranges::view auto as_rvalue( R&& r ); |  | (since C++23)

1) A range adaptor that represents a view of underlying `view` whose elements are rvalues.
2) RangeAdaptorObject. Let e be a subexpression and let T be decltype((e)). Then the expression views::as_rvalue(e) is expression-equivalent to:

- views::all(e), if it is a well-formed expression, T models `input_range`, and std::same_as<ranges::range_rvalue_reference_t<T>, ranges::range_reference_t<T>> is true;
- as_rvalue_view{e} otherwise.

### Data members

Member object | Definition
`base_` (private) | The underlying view of type `V`. (exposition-only member object*)

### Member functions

(constructor) | constructs an `as_rvalue_view` (public member function)
base | returns the underlying view `V` (public member function)
begin | returns the beginning iterator of the `as_rvalue_view` (public member function)
end | returns the end iterator of the `as_rvalue_view` (public member function)
size | returns the size of the view if it is bounded (public member function)
##### Inherited from std::ranges::view_interface
empty | returns whether the derived view is empty. Provided if it satisfies `sized_range` or `forward_range`. (public member function of `std::ranges::view_interface<D>`)
cbegin (C++23) | returns a constant iterator to the beginning of the range. (public member function of `std::ranges::view_interface<D>`)
cend (C++23) | returns a sentinel for the constant iterator of the range. (public member function of `std::ranges::view_interface<D>`)
operator bool | returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of `std::ranges::view_interface<D>`)
front | returns the first element in the derived view. Provided if it satisfies `forward_range`. (public member function of `std::ranges::view_interface<D>`)
back | returns the last element in the derived view. Provided if it satisfies `bidirectional_range` and `common_range`. (public member function of `std::ranges::view_interface<D>`)
operator[] | returns the `n`th element in the derived view. Provided if it satisfies `random_access_range`. (public member function of `std::ranges::view_interface<D>`)

## std::ranges::as_rvalue_view::as_rvalue_view

as_rvalue_view() requires std::default_initializable<V> = default; | (1) | (since C++23)
constexpr explicit as_rvalue_view( V base ); | (2) | (since C++23)

1) Value-initializes `base_` via its default member initializer (= V()).
2) Initializes `base_` with std::move(base).

### Parameters

base | - | a view

## std::ranges::as_rvalue_view::base

constexpr V base() const& requires std::copy_constructible<V>; | (1) | (since C++23)
constexpr V base() &&; | (2) | (since C++23)

Returns the underlying view.

1) Copy-constructs the result from the underlying view. Equivalent to return base_;.
2) Move-constructs the result from the underlying view. Equivalent to return std::move(base_);.

## std::ranges::as_rvalue_view::begin

constexpr auto begin() requires (!/*simple-view*/<V>); | (1) | (since C++23)
constexpr auto begin() const requires ranges::range<const V>; | (2) | (since C++23)

1,2) Returns std::move_iterator(ranges::begin(base_)).

## std::ranges::as_rvalue_view::end

constexpr auto end() requires (!/*simple-view*/<V>); | (1) | (since C++23)
constexpr auto end() const requires ranges::range<const V>; | (2) | (since C++23)

1) Returns std::move_iterator(ranges::end(base_)) if `V` models `common_range`, otherwise std::move_sentinel(ranges::end(base_)).
2) Returns std::move_iterator(ranges::end(base_)) if `const V` models `common_range`, otherwise std::move_sentinel(ranges::end(base_)).

## std::ranges::as_rvalue_view::size

constexpr auto size() requires ranges::sized_range<V>; | (1) | (since C++23)
constexpr auto size() const requires ranges::sized_range<const V>; | (2) | (since C++23)

Returns the size of the view if the view is bounded.

1,2) Equivalent to return ranges::size(base_);

### Deduction guides

template< class R > as_rvalue_view( R&& ) -> as_rvalue_view<views::all_t<R>>; |  | (since C++23)

### Helper templates

template< class T > constexpr bool enable_borrowed_range<std::ranges::as_rvalue_view<T>> = ranges::enable_borrowed_range<T>; |  | (since C++23)

This specialization of `std::ranges::enable_borrowed_range` makes `as_rvalue_view` satisfy `borrowed_range` when the underlying view satisfies it.

### Notes

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_lib_ranges_as_rvalue` | `202207L` | (C++23) | `std::ranges::as_rvalue_view`

### Example

Run this code

    #include <algorithm>
    #include <iostream>
    #include <ranges>
    #include <string>
    #include <vector>

    int main()
    {
        std::vector<std::string> words =
            {"the", "quick", "brown", "\N{FOX FACE}", "ate", "an", "archeopteryx"};
        std::vector<std::string> new_words;

        std::ranges::copy(
            words | std::views::as_rvalue,
            std::back_inserter(new_words)); // move string from words into new_words

        auto quoted = std::views::transform([](auto&& s) { return "“" + s + "”"; });

        std::cout << "Words: ";
        for (auto&& word : words | std::views::as_rvalue | quoted)
            std::cout << word << ' ';

        std::cout << "\nNew words: ";
        for (auto&& word : new_words | std::views::as_rvalue | quoted)
            std::cout << word << ' ';
    }

Possible output:

    Words: “” “” “” “” “” “” “”
    New words: “the” “quick” “brown” “🦊” “ate” “an” “archeopteryx”

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 4083 | C++23 | views::as_rvalue used to accept non-input ranges | made rejected

### See also

iter_move (C++20) | casts the result of dereferencing an object to its associated rvalue reference type (customization point object)
move_iterator (C++11) | iterator adaptor which dereferences to an rvalue (class template)
move_sentinel (C++20) | sentinel adaptor for std::move_iterator (class template)
ranges::as_const_viewviews::as_const (C++23) | converts a `view` into a `constant_range` (class template) (range adaptor object)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/ranges/as_rvalue_view&oldid=177964"